3、当一个节点的所有子节点都没有被选中时，该节点也没有被选中。

4、当一个节点的所有子节点中有一个被选中时，则该节点也被选中。

代码中对事件参数e.Action的判断，可以避免在改变节点的Checked的状态时，再次进入AfterCheck()，这样当在AfterCheck()中有其他逻辑响应时，可以做到每次勾选时，其他逻辑也只响应一次。

参考代码：

        private void treeView_AfterCheck(object sender, TreeViewEventArgs e)
            //通过鼠标或者键盘触发事件，防止修改节点的Checked状态时候再次进入
            if (e.Action == TreeViewAction.ByMouse || e.Action == TreeViewAction.ByKeyboard)
                SetChildNodeCheckedState(e.Node, e.Node.Checked);
                SetParentNodeCheckedState(e.Node, e.Node.Checked);
        //设置子节点状态
        private void SetChildNodeCheckedState(TreeNode currNode, bool isCheckedOrNot)
            if (currNode.Nodes == null) return; //没有子节点返回
            foreach (TreeNode tmpNode in currNode.Nodes)
                tmpNode.Checked = isCheckedOrNot;
                SetChildNodeCheckedState(tmpNode, isCheckedOrNot);
        //设置父节点状态
        private void SetParentNodeCheckedState(TreeNode currNode, bool isCheckedOrNot)
            if (currNode.Parent == null) return; //没有父节点返回
            if (isCheckedOrNot) //如果当前节点被选中，则设置所有父节点都被选中
                currNode.Parent.Checked = isCheckedOrNot;
                SetParentNodeCheckedState(currNode.Parent, isCheckedOrNot);
            else //如果当前节点没有被选中，则当其父节点的子节点有一个被选中时，父节点被选中，否则父节点不被选中
                bool checkedFlag = false;
                foreach (TreeNode tmpNode in currNode.Parent.Nodes)
                    if (tmpNode.Checked)
                        checkedFlag = true;
                        break;
                currNode.Parent.Checked = checkedFlag;
                SetParentNodeCheckedState(currNode.Parent, checkedFlag);
TreeView隐藏部分节点
WinForm中的TreeView没法根据每个节点的情况设置是否有checkbox，只能用CheckBoxes设置整个树是否有Checkbox，可通过如下方式隐藏部分节点的checkbox。
this.treeView1.CheckBoxes = true;
this.treeView1.DrawMode = TreeViewDrawMode.OwnerDrawAll;
this.treeView1.DrawNode += new DrawTreeNodeEventHandler(treeView1_DrawNode);
隐藏节点：
        void treeView1_DrawNode(object sender, DrawTreeNodeEventArgs e)
            //隐藏节点前的checkbox
            if (e.Node.Level == 0 || e.Node.Level == 1)
                HideCheckBox(this.treeView1, e.Node);
            e.DrawDefault = true;
        [StructLayout(LayoutKind.Sequential, Pack = 8, CharSet = CharSet.Auto)]
        private struct TVITEM
            public int mask;
            public IntPtr hItem;
            public int state;
            public int stateMask;
            [MarshalAs(UnmanagedType.LPTStr)]
            public string lpszText;
            public int cchTextMax;
            public int iImage;
            public int iSelectedImage;
            public int cChildren;
            public IntPtr lParam;
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, ref TVITEM lParam);
        private const int TVIF_STATE = 0x8;
        private const int TVIS_STATEIMAGEMASK = 0xF000;
        private const int TV_FIRST = 0x1100;
        private const int TVM_SETITEM = TV_FIRST + 63;
        private void HideCheckBox(TreeView tvw, TreeNode node)
            TVITEM tvi = new TVITEM();
            tvi.hItem = node.Handle;
            tvi.mask = TVIF_STATE;
            tvi.stateMask = TVIS_STATEIMAGEMASK;
            tvi.state = 0;
            SendMessage(tvw.Handle, TVM_SETITEM, IntPtr.Zero, ref tvi);
TreeView递归加载节点
C#遍历指定文件夹下所有子文件夹及文件并添加到目录树：
    private void Form1_Load(object sender, EventArgs e)
            TreeNode root = new TreeNode();
           //根目录名称
            root.Text = "目录";
           //根目录路径
            GetFiles(@"E:\Tools", root);
            treeView1.Nodes.Add(root);
        private void GetFiles(string filePath, TreeNode node)
            DirectoryInfo folder = new DirectoryInfo(filePath);
            node.Text = folder.Name;
            node.Tag = folder.FullName;
            FileInfo[] chldFiles = folder.GetFiles("*.*");
            foreach (FileInfo chlFile in chldFiles)
                TreeNode chldNode = new TreeNode();
                chldNode.Text = chlFile.Name;
                chldNode.Tag = chlFile.FullName;
                node.Nodes.Add(chldNode);
            DirectoryInfo[] chldFolders = folder.GetDirectories();
            foreach (DirectoryInfo chldFolder in chldFolders)
                TreeNode chldNode = new TreeNode();
                chldNode.Text = folder.Name;
                chldNode.Tag = folder.FullName;
                node.Nodes.Add(chldNode);
                GetFiles(chldFolder.FullName, chldNode);